Carboxylic acids substituted with substantially aliphatic substituents derived from polymerization of lower olefins have been described in the prior art and have many important industrial uses. For example, they can be used as anti-rust agents in various organic media such as normally liquid fuels and lubricating oils. They can also serve as intermediates for the formation of metal salts, esters, and nitrogen-containing products which are useful as viscosity index improvers, dispersants, etc., for oil-based lubricants and normally liquid fuels.
Such carboxylic acids can be prepared by thermally reacting an aliphatic hydrocarbon or halogenated aliphatic hydrocarbon with unsaturated acids or acid derivatives at a temperature above about 200.degree. C. The hydrocarbon typically is an olefin polymer such as polypropene or polybutene having a number average molecular weight above about 200. The rate of conversion of such reactions, however, is low and attempts to improve the conversion rate by increasing the reaction temperature and/or using super-atmospheric pressure results in degradation of maleic anhydride to useless carbon dioxide, water and tarry solids. This results in both waste of the valuable maleic anhydride and contamination of the acylating agent that has been produced.
One method for improving the conversion rate, particularly when using an aliphatic hydrocarbon alkylating agent, involves carrying out the reaction in the presence of chlorine. In many instances, high temperatures and long reaction times are still required. These facts, coupled with the necessity for the use of chlorine which is relatively dangerous to use, as well as being expensive and sometimes in short supply, make it desirable to develop alternative methods for the preparation of substituted carboxylic acids or derivatives, which methods are more economical in their use of chemicals and energy.
One such method has been described in U.S. Pat. No. 3,912,764. It comprises a two-stage process in which an olefin polymer is first caused to undergo a thermal reaction with maleic anhydride to a point short of conversion of all of said maleic anhydride, and subsequently an amount of chlorine less than one mole for each remaining mole of maleic anhydride is added, and the reaction is continued in the presence of said chlorine. While this process is said to be more economical than those previously known since it uses a omical than those previously known since it uses a relatively small amount of chlorine and, to a large extent, can be carried out at relatively low temperatures, it is inefficient in that the product is described as containing on the order of 30% unreacted olefin polymer.
Another process for preparing substituted carboxylic acids is by the reaction of a halogenated high molecular weight polymer of one or more lower olefins with an acidic reagent such as maleic anhydride. Such halogenated polymers are usually made by halogen treatment of a hydrocarbon polymer itself and their production requires an average of at least one mole of halogen per mole of hydrocarbon polymer.
A variant of the halogenated hydrocarbon route to succinic acid acylating agents is the process disclosed in U.S. Pat. Nos. 3,215,707 and 3,231,587. This process comprises first preparing a mixture of high molecular weight hydrocarbon polymer and maleic anhydride and then contacting this mixture, at a temperature of about 140.degree. C. to about 250.degree. C., with at least one mole of chlorine for each mole of maleic anhydride present. The reaction takes place over a period of five hours or more. This process also requires the use of large amounts of chlorine relative to the amount of maleic anhydride incorporated. Since it is well known that chlorine is highly corrosive towards many materials normally used to construct large scale reactors, the presence of large amounts of chlorine usually necessitates the use of special reactor equipment fabricated from high-cost materials. Often the final products from such reactions contain at least 0.4% residual chlorine, which is unnecessary to their function as additives or additive intermediates and may, in some instances, be detrimental to their function.
Published French Application 2,201,309 describes a two-stage process wherein in the first stage an olefin polymer is reacted thermally with maleic anhydride to a point well short of conversion of all the maleic anhydride. In the second stage, an amount of chlorine less than one mole for each mole of maleic anhydride is introduced into the polymer/anhydride mixture to complete the reaction. The product mixtures resulting from this process are described as containing more than 30% unreacted olefin polymer. Since the presence of unreacted olefin polymer in the succinic acid acylating reagents used in commerce performs no known useful function, the process of the '309 published application results in the loss of a valuable petrochemical intermediate. This is particularly true since neither the 309 published application nor the general prior art disclose efficient, economical means for separating unreacted olefin polymer from such carboxylic acids.
In U.S. Pat. No. 4,110,349, substituted carboxylic acids of the type prepared by the alkylation of maleic anhydride with an olefin polymer (e.g., polybutene) are prepared by a two-step method which is more economical and efficient than previously known methods. In the first step, the alkylating hydrocarbon is reacted with an unsaturated dicarboxylic acid or derivative thereof in an amount of the latter equal to about 30-90% by weight of the amount required to afford the desired product, optionally in the presence of a small amount of chlorine. In the second step, additional acid or derivative thereof is added and the reaction is continued in the presence of added chlorine.